The overall goal of this project is to elucidate the pathogenesis of Salmonella gastroenteritis using a new model of infectious colitis. In the US alone, Salmonella enteritis is estimated to affect over a million people per year, with costs exceeding $1.4 billion. Large numbers of domestic and agriculturally important animals are also infected. Despite the enormity of the problem, little is know about the pathogenesis of the enteritis, due to lack of a relevant mouse model for the intestinal form of Salmonella disease. We have recently reported the development of a mouse model of Salmonella colitis with diarrhea that mimics human infection. This model involves oral infection of mice possessing a wild-type natural resistance (Slc11A1 or Nrammp1) locus and pre-treated with kanamycin. Infected mice develop pan-colitis and diarrhea accompanied by alterations in colonic epithelial ion transport physiology. The project will involve a collaborative effort that will integrate studies on the physiologic basis of Salmonella-induced diarrhea, the role of bacterial virulence factors, and the importance of innate immune response pathways. Specific Aim 1 will identify the pathophysiologic mechanisms leading to diarrhea in Salmonella colitis. The approach will involve determining the contributions of changes in epithelial ion transport, barrier function, and motility to the intestinal disease process. The hypothesis that epithelial damage and increased cell turnover affects expression and function of membrane transporters will be tested. Isogenic bacterial virulence mutants will be used to manipulate specific phases of the disease process. Specific Aim 2: to determine the role of the host inflammatory cell response in Salmonella-induced colitis and diarrhea. The approach will use antibody-mediated cell depletion and chemokine receptor mutants to study the role of neutrophil and mononuclear cell infiltration. Specific Aim 3: Analysis of the role of NF-:B in diarrhea and colitis induced by Salmonella infection. Salmonella mutants that alter NF-:B activation will be used in combination with mouse strains with tissue-specific defects in the NF-:B activation pathway to test the hypothesis that decreased NF-:B signaling contributes to Salmonella intestinal disease.